1. Field of the Invention
The present invention relates to an electrolytic capacitor, and particularly to an electrolytic capacitor formed by winding an anode foil, a cathode foil and the like.
2. Description of the Related Art
An electrolytic capacitor formed by winding up an anode foil and a cathode foil with separator paper being interposed represents one form of an electrolytic capacitor.
Here, a method of manufacturing an electrolytic capacitor having a two-terminal (one anode terminal and one cathode terminal) structure representing such a wound-type electrolytic capacitor will now be described. Initially, as shown in FIG. 25, band-shaped anode foil 103 and cathode foil 104 each having a prescribed length and two sheets of separator paper 105, 106 are prepared. For example, an aluminum foil having a dielectric oxide film formed is applied as an anode foil and an aluminum foil is applied as a cathode foil.
An anode lead tab terminal 110 is connected at a prescribed position in a longitudinal direction of anode foil 103, and a cathode lead tab terminal 113 is connected at a prescribed position in a longitudinal direction of cathode foil 104. As shown in FIGS. 26 and 27, a columnar boss portion 116a, a plate-shaped connection portion 116b connected to anode (cathode) foil 103, 104, and a columnar lead 116c serving as an anode (a cathode) terminal are provided in anode (cathode) lead tab terminal 110, 113.
As shown in FIG. 25, anode foil 103, cathode foil 104 and the like are arranged in such a manner that one sheet of separator paper 105 is sandwiched between anode foil 103 and cathode foil 104 and anode foil 103 is sandwiched between one sheet of separator paper 105 and the other sheet of separator paper 106. Then, as shown in FIG. 28, one-end sides of arranged anode foil 103, cathode foil 104 and sheets of separator paper 105, 106 are sandwiched between cores 131a and 131b. Then, by turning cores 131a, 131b clockwise in that state, anode foil 103, cathode foil 104 and the like are wound up from the one-end side, to thereby form a wound-type electrolytic capacitor.
An electrolytic capacitor has an inductance component referred to as equivalent series inductance (ESL). This ESL increases with the increase in a frequency, and then the electrolytic capacitor cannot function as a capacitor. Therefore, an electrolytic capacitor used in a high-frequency region is required to have lower ESL. In addition, an electrolytic capacitor has a resistance component referred to as equivalent series resistance (ESR), and it is required to have lower ESR.
In order to lower ESR and ESL, a multi-terminal electrolytic capacitor including a plurality of lead tab terminals as lead tab terminals is available. A method of manufacturing an electrolytic capacitor having a four-terminal (two anode terminals and two cathode terminals) structure representing such a multi-terminal electrolytic capacitor will now be described.
As shown in FIG. 29, a first anode lead tab terminal 111 and a second anode lead tab terminal 112 are connected at prescribed positions in a longitudinal direction of anode foil 103 respectively, and a first cathode lead tab terminal 114 and a second cathode lead tab terminal 115 are connected at prescribed positions in a longitudinal direction of cathode foil 104 respectively. Anode foil 103, cathode foil 104 and the like are arranged as in the case of a two-terminal electrolytic capacitor, and one-end sides thereof are sandwiched between cores 131a and 131b (see FIG. 28). By turning cores 131a, 131b clockwise in that state, anode foil 103, cathode foil 104 and the like are wound up from the one-end side, to thereby form a capacitor element 102 as shown in FIG. 30.
Then, a cut surface or the like of anode foil 103 and cathode foil 104 of capacitor element 102 is subjected to a prescribed treatment such as chemical conversion treatment. Then, a sealing rubber gasket 122 (see FIG. 31) is attached to capacitor element 102. Capacitor element 102 to which sealing rubber gasket 122 is attached is accommodated in an aluminum case 120 with a bottom (see FIG. 31) having a prescribed size. Then, an open-end side of aluminum case 120 is sealed by pressing in a lateral direction and curling and prescribed aging treatment is performed. Then, a seat plate 124 made of plastic is attached to a curled surface of aluminum case 120. Four openings 124a (see FIG. 31) corresponding to positions of respective lead tab terminals 111, 112, 114, 115 are formed in seat plate 124.
Thereafter, as shown in FIG. 31, each lead 116c protruding through opening 124a in seat plate 124 and serving as an electrode terminal is pressed and bent, to thereby complete an electrolytic capacitor 101 having a four-terminal structure. Patent Document 1 (Japanese Patent Laying-Open No. 2004-179621) represents one of documents disclosing an electrolytic capacitor having a multi-terminal structure including, for example, two to four terminals.
The inventors, however, have found that a conventional electrolytic capacitor having a multi-terminal structure suffers the following problems.
As described above, an electrolytic capacitor used in a high-frequency region in particular is required to have lower ESL. This ESL depends on a pitch between leads of anode (cathode) lead tab terminals, and the pitch is standardized in correspondence with a size of the electrolytic capacitor.
As electronic devices and the like are reduced in size in recent years, electrolytic capacitors are also required to have a smaller size. As shown in FIG. 32, as an electrolytic capacitor has a smaller diameter, a distance PL between two anode lead tab terminals 111 and 112 connected to the anode foil becomes smaller. As distance PL is smaller, plate-shaped connection portion 116b of anode lead tab terminal 111 (see FIGS. 26 and 27) and plate-shaped connection portion 116b of anode lead tab terminal 112 come too close to each other, and it becomes difficult to connect anode lead tab terminal 111 and anode lead tab terminal 112 to anode foil 103 in a stable manner, in view of a mechanism of a manufacturing apparatus. This is also applicable to two cathode lead tab terminals 114, 115.
On the other hand, if an attempt to ensure distance PL is made as shown in FIG. 33 such that plate-shaped connection portions 116b of anode (cathode) lead tab terminals 111, 112, 114, 115 do not come too close to one another, a pitch between the lead of the anode lead tab terminal and the lead of the cathode lead tab terminal that are opposed to each other is increased, which will be described further in detail. In a method of forming a capacitor element by winding up an anode foil, a cathode foil, and the like from a one-end side in a longitudinal direction, in the second lap of winding-up and later, the anode foil and the like are further wound up on a portion of the anode foil and the like that have been wound up so far, and a distance in a radial direction from a point of start of winding (center) becomes greater as winding proceeds.
Therefore, as shown in FIG. 34, a pitch PP between leads 116c of opposing first (second) anode (cathode) lead tab terminals increases. Variation in this pitch PP leads to higher ESL and characteristics as the electrolytic capacitor lower.